The present invention relates generally to the design, installation, and use of particulate filters. More specifically, the present invention relates to the use of such filters for collecting and oxidizing carbonaceous and hydrocarbon compounds that make up particulate exhaust emissions from diesel engines.
The diesel engine is the most efficient power plant among all known types of internal combustion engines. Heavy trucks, urban uses, and industrial equipment are powered almost exclusively by diesel engines all over the world. In Europe, diesel powered cars have been increasingly popular. The diesel engine is a major candidate to become the power plant of the future. However, one of the concerns with regard to diesel engines is emission control and air pollution.
There is no dispute that internal combustion engines contribute to air pollution and have an adverse impact on health and on environmental aspects, such as global warming. This has resulted in a great deal of attention to the quantity and type of emissions from diesel engines. In particular, the emission of nitrogen oxides and diesel particulates are of ever greater concern to diesel engine designers.
In the context of the present invention, a catalyzed diesel filter may be used and an understanding of that technology may be helpful.
The function of the catalyst in a catalyzed diesel particulate filter is to lower the soot combustion temperature in order to facilitate regeneration of the filter by oxidation of accumulated soot under exhaust temperatures experienced during regular operation of the vehicle.
Most catalyzed diesel engine particulate filters utilize monolithic wall-flow substrates which are coated with a catalyst. The catalyst lowers the soot combustion temperature, allowing the filter to effectively xe2x80x9cself-regeneratexe2x80x9d during periods of high exhaust gas temperature. A number of diesel filter catalysts have been developed, including both noble and base metal formulations.
The desire to construct or design a xe2x80x9ccleanablexe2x80x9d particulate filter for diesel engines has been present for several years. One development reported in 1995 by the Karlsruhe Research Center of Germany uses a metal fiber material in a form referred to as a xe2x80x9cfilter candlexe2x80x9d. As reported, particulate filters for diesel engines must be regenerated at regular intervals in order to keep within tolerable limits the exhaust gas back pressure which rises with increasing particulate loading of the filter. The particulates are removed from the filter by electric heating under excess air conditions which burns a majority of the particulates to carbon dioxide (CO2).
Compared to the xe2x80x9ccleanablexe2x80x9d filter design of the present invention, this reported electric heating approach is substantially more complicated and costly. In the context of the present invention, the inventors recognized that EPA regulations will require the use of particulate filters to meet legislated levels. As noted, these particulate filters are used to collect and oxidize carbonaceous and hydrocarbon compounds that make up particulate emissions. Over a period of time, the filter also collects the residuals of the oxidation by-products in the form of ash or other deposits that are not combustible. The ash deposits are collected in the filter channels, resulting in a blockage that will not allow the exhaust gases to pass through the filter. The blockage results in excessive exhaust back pressure that reduces engine performance and can lead to engine shutdown.
In order to address these design and performance issues, laboratory tests were conducted involving the use of ceramic filters (cordierite). These filters were operated on actual diesel engines. What the inventors noticed was that, as the test time increases, the pressure drop across the filter increases even after the combustible carbon particles have been burned. Further investigation showed that the non-combustible material that remained were ash deposits that are by-products of the lube oil additives. The additives are metallic compounds and perform a variety of functions in the lubrication of engine parts. All engines burn, to some degree, lube oil during the combustion process and the ash from those additives is captured by the filter.
In the course of testing, the inventors noticed that some of these deposits were shaken loose during engine operation and, as a result, would fall down through the exhaust pipe that is attached to the filter can. The inventors conceived of and reduced to practice a catch basin that allows for the collection and the subsequent removal of that ash for analysis and/or disposal. Based on this testing, the inventors concluded that the ash would fall out of the filter in a similar manner on a vehicle if the particulate filter were installed in a vertical orientation relative to the normal orientation of the vehicle or diesel engine during use. The vibrations that cause the ash to fall out and be deposited in the catch basin are caused by either the engine operation generally or by vehicle vibrations from bumps in the road and related road roughness, all of which combine to produce the shaking loose of ash deposits from the particulate filter. This realization is what led to the present invention. The only remaining issue was how to incorporate this filter into the exhaust system so that a vertical orientation could be realized, while still enabling access to the catch basis for removal of the ash deposits.
The present invention provides a particulate filter for an exhaust system which is equipped with a catch basin that can be easily removed and cleaned by simply disconnecting the catch basin from the balance of the exhaust system. Basic V-type bands or clamps can be used or similar connections that are typical within the exhaust system field. A related option, and a related embodiment of the present invention, is to include an access port or outlet as part of the catch basin with a removable cover so that a shop vacuum cleaner hose can be attached for removal of the ash which is deposited and collected within the catch basin. The particulate filter of the present invention replaces the muffler in a vertical exhaust system which is typically positioned at the rear exterior of the cab.
An exhaust system for a diesel engine for collection of ash deposits according to one embodiment of the present invention includes a particulate filter for filtering a flow of engine exhaust gas, a catch basin for the collection of oxidation by-products (ash) from the particulate filter, a first conduit connecting the particulate filter to the diesel engine, a second conduit connecting the particulate filter to the catch basin, and a mounting arrangement for connecting the particulate filter in a generally vertical orientation based on the normal orientation of the diesel engine when in use.
One object of the present invention is to provide an improved exhaust system for a diesel engine.
Related objects and advantages of the present invention will be apparent from the following description.